Salamanders and zebrafish have something humans can only wish for: the ability of their heart muscle cells to regenerate on demand. While those animals can regrow their injured body parts, sufferers of heart attack are left to make do with a damaged organ. Scientists in Israel and Australia achieved a major breakthrough, uncovering the pathway to stimulate the division of heart muscle cells—a process that stops in human beings about one week after birth. The key agent is the hormone neuregulin, which successfully triggered the divisions of heart cells in mice. It is expected that research funding is quickly going to flock to that area, allowing humans to benefit from this discovery in about five years.